Tunnel Projects

Devil's Slide Tunnels Project
Pacifica, California

The present Devil’s Slide Tunnel consists of twin bores in rock, constructed along Route 1 in Northern California with a 4,000 ft length. It was the first road tunnel constructed by Caltrans in 40 years using a drill-and-blast method. EMI was the lead geotechnical engineer providing geologic and geotechnical interpretation and design recommendations for the tunnels, portals, soil nail walls, and spoils disposal site. This project won EMI the 2013 Engineering Project Achievement Award from the Orange County Engineering Council.

EMI pioneered a large site investigation program in mountainous terrain in an environmentally sensitive habitat with portable limited-access rigs for deep inclined rock and soil borings with in-hole testing and well installations. Trenches were cut for geologic fault mapping.

EMI produced a Geotechnical Data Report, Geotechnical Interpretive Report, and Geotechnical Baseline Report. Seismic loading criteria were developed based on seismic hazard analyses and earthquake-time histories for tunnel and portal design.

Tunnel support systems were evaluated for geo-static loading, seismic-induced distortion, and key block loading. The state-of-the-art seismic design procedure has been Peer reviewed and adopted by Caltrans as a standard for road tunnel design.

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